high transmittance when the climate is cold. And thus, the energy consumption of air conditioning and heating can be reduced. According to the driving force of transmittance adjustment, smart windows can be mainly divided into thermochromic (TC), [4] photochromic (PC), [5] and electrochromic (EC) window. [6] Compared with passive-type TC and PC windows, EC smart window is active-type smart window, which can reversibly change the transmittance by the electrochemical redox in a switching voltage window. [7] However, external voltage is necessary to power the coloring and bleaching process, which will bring the extra energy consumption. [8] Recently, self-powered EC devices (ECDs) have been developed to reduce the energy consumption. For example, Yang et al. successfully fabricated a self-powered WO 3 -based ECD device by friction nanogenerator, which exhibited significant color change from transparent to light blue. [9] However, it is difficult to obtain sustained and stable energy output from nanogenerators for the long-term serving of smart windows. Solar energy has the advantages of clean, harmless, large reserves, and stable output. [10] A solar-powered EC smart window was realized by Davy et al. using complementary poly(2-acrylamido-2-methyl-1-propane-sulfonic acid) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) materials with excellent stability. [11] Nevertheless, the colored EC windows are cannot spontaneously transfer to full colorless state, and an external voltage is still necessary for bleaching process, which make these devices far from zero-energy consumption. [12] Electrochromic devices (ECDs) with adjustable transmittance have opened new opportunities to the development of smart windows for energy-efficiency building. However, the switching between colored and bleached state of conventional ECD will bring extra energy consumption, the design of highperformance ECD with low consumption is still an elusive goal. To address this issue, a self-driven and energy-saving Ni anode-based ECD using Prussian blue as electrochromic material is developed. During the day, it can be colored by solar energy. By contrast, it can spontaneously bleach when the ECD's anode and cathode are short-circuiting using the internal redox potential during the night. It is worth noting that no extra energy is inputted in the coloring-bleaching cycle. In comparison with the ECD using electrolyte with high Ni 2+ (K + :Ni 2+ = 1:9) or high K + (K + :Ni 2+ = 9:1) concentration with poor optical contrast and cyclic stability (failed <100 cycles), the Ni-based ECD with the electrolyte containing equal amount of K + and Ni 2+ exhibits a high optical contrast (39.45%), good coloration response time (6 s), and excellent stability (1000 cycles). These properties suggest that the Ni-based electrochromic configuration is expected to be a catalyst for the development of energy-storage EC smart window in the future.